In the known embodiments, the ball shutter is constrained to a control rod with a throttle or grip lever fixed at the free end for opening/closing the valve. In practice, it is enough to rotate the throttle or grip lever even just a little to alter the position of the ball shutter and therefore the section of the passage of the fluid. It has been noticed that in some cases, such rotations of the throttle can occur accidentally, for example during plant maintenance, after strong vibrations or by unauthorised people, for example children.